(a) Field of the Invention
The present invention concerns what is claimed in the preamble, and accordingly relates to active optical connections.
(b) Description of the Related Art
Data processing increasingly requires that large volumes of data can be transmitted between different locations; this can be the case within a computer, for instance between the CPU and memories or between the motherboard and hard disks, but also within local networks, for example between workstation computers and local company servers, and also for connection to the Internet. Data transmission is additionally important from those locations at which large volumes of data arise to those locations where they are processed. Experiments appertaining to high-energy physics using particle detectors shall be mentioned by way of example.
The data transmission can take place purely electrically using electrical cables; however, transmission is also possible by means of optical signals. In this case, light signals can be radiated into an optical waveguide, such as a multi-mode fiber, by a modulated light transmitter, for example a laser diode modulated in accordance with the data signals, and can be transmitted by the optical waveguide to a light receiver, such as a photodiode, where the light signals can be converted into electrical signals again and processed. In this case, the desired high transmission rates of optical data connections require that the light generated by the light transmitter is modulated with high frequency and is efficiently coupled into the optical waveguide in order to obtain a good signal-to-noise ratio.
In the case of rapidly modulatable optoelectrical transmission elements such as laser diodes, therefore, it is also necessary to take account of the emission behavior for the quality of the optical connection. What is important is that a greatest possible portion of the light emitted by an active optical transmission element is coupled into the optical waveguide, that is to say typically the multi-mode optical fiber. This is difficult primarily in the case of so-called surface emitting semiconductor lasers, Vertical Cavity Surface Emitting Lasers, VCSELs. The latter emit the laser beam generally in the direction of their surface normals, while a high efficiency of coupling the laser light into the optical waveguide fibers requires that the end faces thereof are arranged transversely with respect to the direction of the beam. On account of the difficult mounting and the typically limited space available, this is generally prohibited, however, if the active optoelectronic transmission element is mounted in a planar fashion on a plane such as a circuit board or some other carrier substrate, because the fiber would have to be perpendicular to the carrier substrate for this purpose.
Since the arrangement of the active optical transmission element perpendicularly to the circuit board is generally likewise not considered, both for space reasons and for mounting reasons, it has already been proposed to arrange a VCSEL or some other optoelectronic element in a planar fashion on a carrier substrate and to conduct away the light parallel to the substrate by means of a suitable optical waveguide fiber; it has likewise already been proposed to provide a deflection means such as a mirror element between the active optoelectronic element and the optical waveguide fiber.
The deflection means can be formed by a reflector. A method and a device for producing an optical connection between an optoelectronic component and an optical waveguide are known, in particular, from DE 10 2004 038 530. Reference is likewise made to the dissertation by Denis WOHLFELD. The cited documents are fully incorporated by reference in the present application.
DE 43 23 681 A1 discloses an arrangement for coupling at least one optical waveguide fiber to at least one optical reception or transmission element and a method for producing the arrangement. In this case, optical waveguide fiber and optical element are intended to be arranged on opposite sides of a common carrier. The optical waveguide fiber is assigned a light beam deflection arrangement in the region of the optical axis. An optically transparent carrier such as a silicon substrate is intended to be used, wherein a guide structure for the optical fiber and a holding structure are intended to be incorporated on opposite sides, which can be done by etching. The fitting of alkali-containing glass to the carrier is mentioned.
JP 2003 131088 discloses an optical module that is intended to provide an optical path between an optical element and an optical fiber. The fiber end and other optical waveguide bodies are intended to be arranged in a V-shaped groove provided on a carrier.
U.S. Pat. No. 5,168,537 discloses a method and a device for coupling light between a waveguide and an optoelectronic device, in which a terminating block has embedded therein a multiplicity of collimating cylindrical lenses protruding from a first end of the block. A plurality of fibers are arranged longitudinally with respect to the lenses and likewise embedded into the block. A deflection block receives this end part and deflects light onto optoelectronic elements. The arrangement is large, has large distances between fiber ends and optoelectronic element and thus has considerable disadvantages.
U.S. Pat. No. 6,389,202 discloses an arrangement in which the optical power emitted by a VCSEL is intended to be coupled into a fiber in the best possible way, that is to say with maximum power transfer. For this purpose, carrier grooves are etched in a silicon substrate, for example by plasma ion etching. A glass cover is intended to be arranged over the grooves, where fibers are then intended to be arranged with high accuracy in the grooves. The glass layer is intended to be particularly smooth, which is intended to make it possible to use the technique of flip-chip bonding for fitting optical components. Inter alia, VCSEL and the like are mentioned among such optical components. A high alignment outlay is still required during mounting in this case.
U.S. Pat. No. 5,764,832 explains that the outlay for mounting optical fibers on plug connectors for optoelectronic communication is very high. It is proposed to provide a groove in a carrier substrate, to form a flat surface on the carrier substrate with the groove and to position an optical component on the flat surface and then to position an optical fiber in the groove. The positioning is intended to be monitored visually. This, too, involves high outlay.